Various kinds of toners are known in which fluorine-containing compounds are provided on the surfaces of toner particles for the purpose of obtaining improved development properties.
For example, JP-A-58-66950 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a capsule toner in which an organic fluorine compound is provided on the capsule surfaces; JP-A-59-181358 discloses a capsule toner in which a fluorine-containing resin is provided on the capsule surfaces; JP-A-60-126657 discloses a capsule toner prepared by using a fluorine-containing compound as one of interfacially polymerizable monomers for forming the shell material; JP-A-61-120160 discloses a capsule toner having electrification properties imparted by reacting a fluorinecontaining alcohol with carboxyl or isocyanate groups present on the shell; and JP-A-63-177145, JP-A-63-177147, and JP-A-63-177148 disclose a capsule toner in which high-molecular chains have been formed on the shell surfaces by graft polymerization of a monomer containing a fluorine atom as a charge-control group.
However, all of the toners described above have been still unsatisfactory. Illustratively stated, the toner disclosed in JP-A-58-66950 is disadvantageous in that the independence of electrification on the environment, especially on humidity, is poor because the organic fluorine compound used therein contains, in each molecule thereof, a hydrophilic group besides a hydrophobic group including the fluorine atom. The toner disclosed in JP-A-59-181358 is defective in that since the fluorine-containing resin used is a polymer or copolymer whose structure is the same as hydrocarbon substituted with fluorine atoms, the adhesion between the resin and the capsule shells is so poor that the resin readily peels off. The capsule toner disclosed in JP-A-60-126657 has a drawback that it is difficult to attain satisfactory properties with respect to both the mechanical properties of shells and the electrification properties of toner by use of the same shell material and, hence, latitude in selection of the shell materials is narrow. The toner disclosed in JP-A-61-120160 has the following problems. In the case where capsule shells are formed by way of interfacial polymerization, it is difficult to allow carboxyl or isocyanate groups to be present on the shell surfaces because both of these groups are functional groups that take part in interfacial polymerization. Further, the reactions of these functional groups with an alcohol do not sufficiently proceed in an aqueous solution, resulting in necessity of use of an organic solvent. Therefore, a solvent-recovery apparatus should be provided and the production equipment should be explosion-proofed, increasing the production cost of the toner. The toner disclosed in JP-A-63-177145, JP-A-63-177147, and JP-A-63-177148 is disadvantageous in that vinyl fluoride, which is the only example shown therein as the monomer containing a fluorine atom, is gaseous at room temperature and, hence, grafting of such vinyl fluoride onto capsule surfaces necessitates a special reactor.
It has further been proposed to maintain the electrification stability of a toner by use of a metal complex or the like. However, this technique has many disadvantages. For example, it is difficult to control the dispersion of a metal complex in a toner, and since metal complexes generally have colors, they cannot be used with colored toners.